 A total of 129 Japanese prisoners and a number of local residents and guerrillas were held in the prison at that time.The destruction of the town and the fortress and the execution took place after the evacuation of the entire population due to the offensive of the Japanese army.The Nikolayevsk incident was used by Japan as a pretext to justify the retroactive occupation of Northern Sakhalin, which was occupied by the Japanese on 22 April 1920.